Auxetic frameworks inspired by cubic crystals

In this work we show that a structure consisting of a network of bending beams can exhibit a negative Poisson’s ratio. We have shown that the negative Poisson’s ratio behaviour is driven by the (bcc analogous) type III beams, the type II (fcc like) beams result in a structure with a Poisson’s ratio of around zero and type I (simple cubic configuration) beams result in a Poisson’s ratio of nearly +1. The tensile and shear strengths of the type III beams are augmented by addition of type II and type III beams. By tailoring the relative stiffness of the component beams within the structure it is possible to design an auxetic truss structure with specific Poisson’s ratio, tensile and shear moduli.This validates the hypothesis that crystal structures can provide inspiration for macro structures with tailored mechanical properties where the mechanism for negative Poisson’s ratio (auxetic) behaviour at the atomic scale in cubic crystals is replicated by bending beams.